Many methods and apparatus are known which are employed for mixing two fluids. In many of these a low pressure area is created in a first fluid, and a second fluid to be mixed with the first fluid is admitted to the low pressure area. In processes which relate to gasification of a fluid, one method employs a venturi to create a pressure lower than atmospheric to pull air into a flowing fluid stream.
One such shown in U.S. Pat. No. 3,853,271 (Freshour et al). This system includes a plurality of cup-shaped members. A fluid flows through the central portions of the members, and a low pressure area is pulled in from the exterior of the cups to mix with the flowing fluid Another such venturi system is shown in U.S. Pat. No. 4,017,565 (Muller). This patent shows a system for mixing a gas with a liquid wherein a pump circulates a liquid in a container. The liquid is pumped through a cylindrically symmetric baffle which provides an annular constriction for increasing the velocity of the circulating liquid. This increased velocity creates the venturi effect whereby air from a tube aligned with the axis of the baffle is admitted to the flowing liquid.
Venturi systems have several drawbacks which particularly prevent efficient mixing of a gas with a liquid. A venturi system requires a large duct-to-throat area-ratio to create the low pressure required to induce air. A duct-to-throat ratio of 5 is not uncommon, and this means that the kinetic energy in the throat is 25 times that in the duct. The subsequent reduction in flow velocity in the diffuser results in large flow losses which prevents recovery of the kinetic energy investment made in the throat. Further, the air inducted in the throat is usually composed of large bubbles which must be transported through the diffuser and broken up by additional elements, such as a pump impeller, if the gas-liquid surface area is to be increased.
It is also known to provide a vortex for pulling air into a fluid. U.S. Pat. No. 4,259,267 (Wang) shows an apparatus wherein a single propeller is located in a fluid beneath a plurality of vertical, cylindrical tubes. As the propeller pulls the fluid through the tubes, a vortex develops in each tube thus entraining gas into the center of each vortex.
It is further known to simply pump air under pressure into a body of fluid. U.S. Pat. No. 3,643,403 shows an apparatus wherein air is pumped to a disperser located in the body of the fluid. An impeller is located above the disperser and circulates fluid so that bubbles which are emitted from the disperser flow downwardly with the fluid flow to thereby increase the time of contact of the bubbles with the fluid. U.S. Pat. No. 2,479,403 shows a system wherein aeration of sewage is effected by the action of a submerged water-jet injector. British Patent 1,484,657 shows a system wherein air is injected under pressure into a downwardly flowing stream so that the contact time of air bubbles with the fluid is increased.
The common faucet aerator is also known wherein flowing water is caused to be turbulent so that air is drawn in by a process similar to the injector effect. U.S. Pat. No. 4,214,702 (Shams et al.) shows such a faucet aerator.
Another aerator, shown in U.S. Pat. No. 2,295,391 (Derden, Jr.) uses a pump to circulate fluid between a container and a chamber containing a gas. The fluid flows turbulent mixing of the fluid with the gas.
Another aeration apparatus is shown in U.S. Pat. No. 3,591,149 (Auler). This apparatus includes a plurality of blades which rotate about a single vertical axis. The blades are elongate and extend into the fluid so that when the blades are rotated, fluid flows in an upward direction along one side of each blade. The resulting turbulence causes aeration of the fluid.